This invention generally relates to air intake heating systems for internal combustion engines, and is specifically concerned with a speed dependent air intake heater for use with a diesel engine that maximizes the reduction of white smoke emissions while minimizing the depletion of the battery during cold start-up condition.
Air intake heating systems and methods for reducing white smoke emissions of diesel engines during cold start-up conditions are known in the prior art. The purpose of these systems is to reduce the generation of white smoke when a diesel engine runs under no load or light load conditions at low temperature. Such white smoke is the result of unburned hydrocarbons in the engine exhaust and is attributable to the incomplete combustion of the diesel fuel in some or all of the engine cylinders due to misfiring. While white smoke is not a regulated exhaust emission, it is a respiratory and optical irritant and can have an adverse effect on driver visibility.
One of the most recent advances in white smoke reducing systems is disclosed in Trotta et al U.S. Pat. No. 5,094,198, assigned to the Cummins Electronic Company. In this system a microprocessor has an input that receives a signal from an intake manifold air temperature monitoring sensor, and an engine speed monitoring sensor, and an output that controls the actuation of electrically powered air heating elements that are actuated and deactuated to heat the intake air. The pattern of actuation and deactuation of the electrical air heating elements is dependent upon various combinations of sensed engine operation, sensed intake manifold air temperature and sensed battery condition. Depending upon whether the speed sensor indicates that the engine is in a cranking state, a running state, or a warmed state, the microprocessor of this system will admit different amounts of power to the heating elements.
While the air intake heating device disclosed in the '198 patent functions well in small, direct injection diesel engines used in marine applications, the applicants have observed some areas where such a device might be improved when applied to later-generation diesel engines of the type used to drive tractor trailers and other heavy equipment. Specifically, while the applicants observed that the system disclosed in the '198 patent was capable of substantially reducing white smoke emissions in such engines under cold weather conditions, it did so by making large demands on battery output. Since the battery used in such engines generally cannot be recharged by the engine alternator when cold, such a large power demand can deplete the battery charge to such an extent that the life of the battery is significantly shortened.
Clearly, what is needed is an improved air intake system and method that is capable of reducing white smoke emissions of a diesel engine to acceptable levels throughout the entire operating range of the engine without significantly shortening the life of the engine battery. Ideally, such a system should be relatively simple in structure, and inexpensive to manufacture and to install in a variety of diesel engines. It would also be desirable if such a system and method could be easily retrofitted in engines that already have some sort of microprocessor-based controller for heating the intake air of the system.